1. Field of the Invention
The present invention generally relates to semiconductor devices and in particular to a semiconductor optical device having a variable refractive index profile.
With the development of optical telecommunications systems using optical fibers as a means for transmitting information, the need for various high speed optical switching devices is becoming an acute problem. For example, the concept of an optical switching system as shown in FIG. 1 has been proposed, wherein light beams produced by a semiconductor laser array 1 are guided along optical fibers 2 each having branched ends on which optical couplers 3 are provided, and these optical couplers 3 are coupled respectively with corresponding optical couplers 5 via an optical gate array 4. Each of the optical couplers 5 is connected to an optical fiber, and the optical fibers are assembled into a reduced number of optical fibers 6 which in turn are connected to a photodetector array 7. The optical gate array 4 selectively allows the passage of the optical beam from the optical coupler 3 to the corresponding optical coupling element 5, and thus optical switching within the telecommunication network is achieved.
In such an optical gate array, the use of a semiconductor material wherein the transmittance of light changes in response to the carrier density therein has been considered for switching the optical beam. The transmittance in such a semiconductor material is reduced in response to injection of carriers and is increased in response to a depletion of the carriers therein. However, such a semiconductor material may lose the capability of switching the optical beam when subjected to a light having a large intensity, since strong light increases the transmittance unconditionally.
In order to avoid the foregoing problem, the use of a movable lens system as shown in FIG. 2 has been considered. Such a movable lens system is used commonly in conventional optical disk recording systems such as compact disk players and comprises a lens 8 held movably on a magnetic or piezoelectric actuator device 9. When using this system in connection with a gate array 4, the lens 8 and the actuator 9 are disposed in a row and column formation in correspondence to the optical couplers 3 and 5, and optical switching occurs in response to the movement of the lens 8. Thus, when the lens 8 is in a focusing state with respect to the optical couplers 3 and 5 as shown in FIG. 2, the optical beam in the coupler 3 is transferred to the optical coupler 5. On the other hand, when the lens 8 is offset in either direction relative to the optical coupler 3 or to the optical coupler 5, the transfer of the optical beam is interrupted.
Such a system, although capable of operating properly even when subjected to a strong light, has an obvious problem in that it relies upon mechanical movement of the lens 8 for the optical switching and thus has a problem of slow response due to the mechanical inertia of the lens 8. Thus, the use of such mechanical system for optical gate array systems of optical telecommunication systems or for future optical computers is out of the question.
An optical device which is capable of changing the focal length of the lens or capable of deflecting an optical beam in response to a control signal at a high speed is demanded. Such an optical device would be useful also in other optical systems such as in compact disk players or laser printers wherein the laser beam must be focused on a rotary body rotating at a high speed while maintaining a proper focusing state.